Capacitance-based occupant detection devices are known and in particular serve for distinguishing between a children's seat located on a vehicle seat and an adult sitting on the vehicle seat. For use in the USA, these occupant detection devices must in particular satisfy the requirements of FMVSS 208 (Federal Motor Vehicle Safety Standard). In this connection, it should in particular be ensured that the airbag or airbags associated with the front passenger seat is/are not triggered in the case of small children at an age of up to one year.
With such a capacitance-based occupant detection device, an antenna, which is arranged beneath the seat surface in the seat cushion and which is operated at an AC voltage with a frequency of 50 kHz, is used to satisfy the named distinguishing function. If a person sits in the vehicle seat, a coupling results between the person and the antenna which has the result that a transmitted radiation moves through the person to the vehicle chassis at which the respective field strength is measured. If a children's seat is located on the vehicle seat or if said vehicle seat is empty, no such coupling arises.
However some problems occur in connection with such capacitance-based occupant detection devices. Such a device is, for instance, not able to distinguish between an empty vehicle seat and an occupied vehicle seat. In addition, the device is also influenced by moisture in an unwanted manner. Water on the vehicle cushion or a damp cushion can thus, for example, effect an appreciable coupling toward the chassis. If a children's seat is located on a wet seat, the classification which is carried out may thus fail.